meta: update mailmap/AUTHORS info for existing collaborator

Use the same email address in AUTHORS, README.md, and git metadata for
existing collaborator.

.mailmap

@@ -531,6 +531,8 @@ xiaoyu <306766053@qq.com>
 Xu Meng <dmabupt@gmail.com> <mengxumx@cn.ibm.com>
 Yael Hermon <yaelherm@gmail.com> <yaelhe@wix.com>
 Yang Guo <yangguo@chromium.org>
+Yash Ladha <yash@yashladha.in> <18033231+yashLadha@users.noreply.github.com>
+Yash Ladha <yash@yashladha.in> <yashladhapankajladha123@gmail.com>
 ycjcl868 <45808948@qq.com> <chaolinjin@gmail.com>
 Yingchen Xue <yingchenxue@qq.com>
 Yongsheng Zhang <zyszys98@gmail.com>

AUTHORS

@@ -3027,7 +3027,7 @@ Christian Niederer <aqpoba@gmail.com>
 Sk Sajidul Kadir <sheikh.sajid522@gmail.com>
 Bartlomiej Brzozowski <bart.brzozowski@janeasystems.com>
 Saajan <saajan.sn@gmail.com>
-Yash Ladha <yashladhapankajladha123@gmail.com>
+Yash Ladha <yash@yashladha.in>
 Alex R <alexei.rudenko@gmail.com>
 Hachimi Aa (Sfeir) <hachimi.aa@sfeir.com>
 Daniel Estiven Rico Posada <danielrico.posada@gmail.com>